Various means are known in the art for storing a significant quantity of ink in an ink bag or other container in an ink-jet printer and supplying it in smaller quantities to an ink bladder. For instance, an ink delivery system has been developed which is provided with a reservoir for supplying a refillable bladder. The bladder is then used to feed the printhead, and when the bladder is depleted, it is refilled from the reservoir or ink bag. The system utilizes a three-way valve which permits selective fluid communication between the ink bag and the bladder (refill mode) and between the bladder and the ink-jet printhead (print mode). A third position (shipping mode) prevents fluid communication between any of the compartments. U.S. Pat. No. 4,714,937 describes and claims this system.
In the embodiment illustrated in the patent, the ink bag and the ink bladder are shown mounted side by side on a support platform; the three-way valve and fluid communicating channels are located under the top surface of the platform. The ink flows out of the bottom of the ink bag and into a short vertical channel; then it flows horizontally to the three-way valve; next, with the valve in the refill mode, it flows through the valve into a vertical channel and up into the ink bladder. When the valve is turned to the print mode, the ink flows out of the bottom of the bladder through the vertical channel to the three-way valve, then through the valve into another channel to the printhead.
In another arrangement, not illustrated in the patent but illustrated in copending application Ser. No. 07/390,807, filed Aug. 8, 1989, which has the same assignee as this application, the ink bag is mounted on the platform and the ink bladder is suspended from the platform and is at a level below the ink bag. With the valve in the refill mode, ink flows out of the bottom of the ink bag into a vertical channel, then into the three-way valve where it is diverted into a horizontal channel to the ink bladder. When the three-way valve is turned to the print mode, ink returns through a horizontal channel (the vertical channel in the refill mode) to the three-way valve, where it is now diverted into another channel to the printhead.
A problem associated with both of these systems occurs when the ink supply is depleted. This allows the air, which tends to accumulate in the ink bag, to enter the bladder, from which the air needs to be removed. This task increases the complexity and cost of the product. When this happens, the bladder will refill with air rather than ink. This results in a printing failure.